The present invention relates to a new and improved construction of apparatus for manufacturing boxless casting mold parts.
There are known to the art boxless casting molds composed of an upper part and a lower part, sometimes referred to as an upper mold half and a lower mold half. In contrast to casting molds in boxes or flasks they have the appreciable advantage that there is avoided the pronounced wear to which the molding boxes are subjected in the foundry during the circulation thereof through the foundry. On the other hand, they are associated with the drawback that, especially with markedly different pattern heights during the conventional automatic fabrication thereof, the molding sand, during compaction by means of a pressure or compaction plate, is only sufficiently, i.e., maximumly compacted at the regions above the high pattern parts, whereas at the remaining regions there is only produced an insufficient compaction of the molding sand. The different compaction of the mold parts therefore frequently leads to casting flaws or defects at the casting.
To avoid such defects it has already been proposed, following the compaction operation by means of the pressure plate, to subject the casting mold part to a post-compaction at the opposite side by raising the pattern support. However, in practice this technique only constitutes an apparent improvement, since during pre-compaction the sand region above the high pattern parts already has reached the threshold value of compaction. During post-compaction this threshold value is rapidly attained, if it has not already been reached during pre-compaction, so that the aforementioned sand region resists any further compaction. Consequently, the unsatisfactorily compacted sand region only can be post-compacted to a minimum degree or not at all.
During the manufacture of casting molds in flasks or boxes, when working with different heights of the pattern contours, the pressure plate is subdivided into a number of individually effective press punches. Each of these press punches only compacts a small region of the molding sand. In this way there is obtained an extremely uniform and good compaction of the entire mold part, wherein, however, corresponding to the pattern contour, there are formed higher and lower situated sand sections. Since, however, during the compaction operation there is still present the sand filling frame which has been placed upon the molding box or flask, after the removal of such frame there can be severed the sand sections protruding past the box edge, whereas the sections which are situated lower than the box edge do not disturb. Yet, the multi-punch system which has been found to be quite advantageous during the compaction of mold parts in flasks or boxes is unsuitable however for boxless mold parts, because the compaction occurs within the mold box or flask itself, and thus, the different height sand sections all are located below the mold box edge and cannot be severed or removed. Following the ejection out of the mold box, which is already difficult owing to the contour of the sand, there is thus missing at the lower mold part the flat standing surface needed for the further transport and at the upper mold part the flat support or contact surface for the weighting plate or the like.